Another great example of the interaction between wild and domesticated biodiversity. As the rain forest is cleared for ranching in Latin America, its blood-sucking bats are increasingly turning from tapirs and the like to cattle as something juicy to sink their teeth into. This is also leading to an uptick in rabies cases among humans.
Food composition
The new issue of the Journal of Food Composition and Analysis has reviews of food composition activities in both Latin America and Oceania. I only have access to the abstracts, but I know that in the Pacific a lot of attention is being paid to differences in nutrient composition among varieties of crops like banana, pandanus and giant swamp taro. This is something that might be of interest to the authors of a third paper in the same issue of the journal. They look at differences in micronutrient composition within different cereal species in Mali but fail to mention this varietal dimension. They ascribe the differences to climate and ecology — at least in the abstract. Important, of course, but surely not the whole story. I’m going to try to get hold of the paper.
LATER: So it looks like what they did is collect various different samples of fonio, say, in each of several distinct eco-geographic zones and pool the samples collected in each zone for analysis. Nothing in the paper about trying to collect material with similar varietal names or anything like that. So any differences due to environment will be confounded with genetic variation. Seems to me like an opportunity missed, at best.
Fido decoded
An article by Elaine Ostrander in the latest American Scientist summarizes recent advances in canine genomics, which have been considerable:
The dog genome has been mapped and sequenced. A host of disease loci have been mapped, and in many cases the underlying mutations identified. Our understanding of how dog breeds relate to one another is beginning to develop, and we have a fundamental understanding of the organization of the canine genome. The issue of complex traits is no longer off-limits. We have begun to understand the genetic portfolio that leads to variation in body size and shape, and even some performance-associated behaviors.
Some snippets:
- Between-breed genetic variation is about 27.5% of the total, compared to about 5% between human populations.
- Dog breeds fall into 4 main groups: Asian and African dogs, plus grey wolves; mastiffs; herding dogs and sight hounds; and modern huntings dogs.
- 75% of the 19,000 genes that have been identified in the dog genome show close similarities with their human counterparts.
- Variation in a single gene (IGF1) explains a lot of the size differences among and within breeds.
What to do with all this information?
It is certainly hoped that the disease-gene mapping will lead to the production of genetic tests and more thoughtful breeding programs associated with healthier, more long-lived dogs. It will be easier to select for particular physical traits such as body size or coat color… Finally, canine geneticists will have a chance to develop an understanding of the genes that cause breed-specific behaviors (why do pointers point and herders herd?).
Mayan manioc
Signs of a cassava field have been found under the several metres of ash that buried a Mayan village when a nearby volcano erupted in about 590 AD. Archaeologists excavating Ceren in San Salvador — dubbed the American Pompeii — found tubular hollows in the solidified ash, formed when the tubers decomposed. This is apparently the earliest evidence of cassava cultivation.
Backyard domestication
There’s a “dump heap” hypothesis of agricultural origins which suggests that people first got interested in actively managing and manipulating plants for food or other products when they saw them sprouting out of piles of garbage in and about settlements. There they could observe them daily and experiment with them. A slight variation on this theme — involving corrals in pastoralist campsites rather than garbage dumps — has been proposed for the domestication of quinoa.
One of the things that might have happened in these fertile micro-environments in close proximity to human habitations is that different related species might have been brought accidentally together, leading to hybridization and the development of interesting new — polyploid — types. But there really hasn’t been much empirical evidence for this.
No more. A new paper ((Colin E. Hughes, Rajanikanth Govindarajulu, Ashley Robertson, Denis L. Filer, Stephen A. Harris, and C. Donovan Bailey. Serendipitous backyard hybridization and the origin of crops. PNAS published August 17, 2007, 10.1073/pnas.0702193104.)) looks at the domestication of the legume tree Leucaena in Mexico, where it is grown for food (it is also used as a fodder in some parts of the world). A variety of evidence is discussed which suggests that there has indeed been much hybridization among up to 13 different wild species of Leucaena in Mexican backyards. This has proved “a potent trigger for domestication.” The authors think a similar thing also happened in Mexico with two other perennial crops, Agave and Opuntia.